1. Field of the Invention
The present invention relates to a tracking servo system for use in an information recording disc playing apparatus, and more specifically relates to a tracking servo system performing a jump operation for jumping recording tracks on the disc.
2. Description of Background Information
With apparatus for playing an information recording disc (simply referred to as "disc" hereinafter) such as a video disc or a digital audio disc, it is necessary to use a tracking servo system for controlling the position of the information reading spot of the pickup so that it accurately follows the recording track irrespective of the eccentricity of the disc, for example.
This tracking servo system constitutes a so-called closed loop system which generates a tracking error signal corresponding to the amount of deviation of the information reading light spot with respect to the recording track of the disc in a disc's radial direction, and performs position control relative to the recording track by driving an actuator for moving the information reading spot in the radial direction in response to the tracking error signal. Furthermore, in the case of such a servo system, the servo loop is opened during the so-called jump operation for jumping recording tracks, and an acceleration pulse is applied to the actuator while the servo loop is opened, a deceleration pulse is then applied to the actuator at a predetermined time in the jump operation, and afterwards the servo loop is made closed at an appropriate time so as to pull-in (or lock-in) the servo loop.
In this track jump control, the pulse width and the pulse height of the acceleration and deceleration pulses are determined according to the pitch of the recording tracks, since the track pitch is generally equal to a standard value. However, in some cases there are nonstandard discs in which a sudden change in the track pitch can occur. If the track jump operation is performed while playing a nonstandard disc, the acceleration would become excessive, for example, if an acceleration pulse having the normal pulse width and the normal pulse height is applied at a position where the track pitch is reduced suddenly. In such a case, the amount of jump of the information reading point becomes excessive with respect to the track pitch, and it renders the jump operation unstable.